Keeper for a dental magnetic attachment

ABSTRACT

The aim of the present invention is to offer a keeper for a dental magnetic attachment that is strong, has low manufacturing costs, and is not easily detached from the tooth root. The keeper proposed herein has a keeper body, which is shaped like a plate, and a root, which is attached to the bottom of the keeper body. The keeper body and the root are machined from a single piece of soft magnetic material in one piece. The root has a smaller diameter part that is linked to a larger diameter part whose external diameter is larger than an external diameter of the smaller diameter part. The smaller diameter part is linked to the bottom of the keeper. There are multiple circumferential grooves around the outer side of the larger diameter part.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2002-281636, filed Sep. 26, 2002, entitled “AKEEPER FOR A DENTAL MAGNETIC ATTACHMENT”. The contents of thisapplication are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a keeper of a dental magneticattachment that fixes a denture by using magnetic attractive force.

2. Discussion of the Background

A dental magnetic attachment that fixes a denture by using magneticattractive force has already been developed in the dental field. Theprior dental magnetic attachment 9, as shown in FIG. 3, comprises amagnetic assembly 91 embedded in a denture 81 and a keeper 92 embeddedin a root cap 82 to contact the magnetic assembly 91. The keeper 92 ismade of soft magnetic material that generates attractive force betweenthe keeper 92 and the magnetic assembly 91.

The dental magnetic attachment in this structure requires the conditionthat the keeper 92 is cast in the root cap 82. The casting process inwhich the keeper 92 is incorporated into the root cap 82 requiresprecise control of casting conditions at an elevated temperature tomaintain the good quality of the keeper 92. The process requires a lotof time and is prone to various problems. As the result, the cost ofkeeper preparation is increased significantly. It also prolongs themedical treatment period for the patient.

Therefore, recently, a keeper is cemented directly on the tooth rootsurface using advanced dental resin that has been developed. This typeof keeper 92, as is shown in FIG. 4, comprises a keeper body 921 and aroot 922 which are linked together by welding. (cf. Unexamined patentapplication publication 2000-137260)

However, the keeper 92 mentioned above faces the following difficulties.

As mentioned above, in the keeper 92, the keeper body 921 and the root922 are connected by welding. The root 922 is sometimes referred to as apost. Therefore the welding process, which takes a lot of time andlabor, makes it difficult to decrease the cost of the keeper. The weldedstructure itself has no special problem in strength, but because of thenature of welding, it is not possible to overcompensate very much onweld strength so there is not much leeway when it comes to strength. Sothe strength of the border between the keeper body and the root part,that is, the strength of the keeper has been required to be elevated.

The prior keeper 92, as is shown in FIG. 4, has an excellent structurethat has a smaller diameter bendable part 923 and that enables the root922 to be bendable. Moreover, a step part between the bendable part 923and larger diameter taper part 924 prevents embedded keeper 92 fromcoming off.

But the step part is not enough to prevent the keeper 92 from coming offand more excellent structure to prevent coming off has been required.

SUMMARY OF THE INVENTION

Considering these difficulties, the present invention provides a keeperfor the dental magnetic attachment that is low in manufacturing cost,and is superior in prevention of coming off and strength.

The present invention is directed to a keeper of dental magneticattachment so as to be attracted by a magnetic assembly embedded in adenture base.

This keeper includes a keeper body which is shaped like a plate and aroot positioned on the bottom of the keeper body. The keeper body andthe root are made of the same soft magnetic material and are machinedfrom a single piece of soft magnetic material to make the keeper in onepiece.

In the root, a smaller diameter part is linked to a larger diameter partwhose external diameter is larger than an external diameter of thesmaller diameter part, and the smaller diameter part is also linked tothe bottom of the keeper body.

The outer side of the larger diameter part has multiple circumferentialgrooves that are made circumferentially.

In this keeper, as is mentioned above, the keeper body and the rootpositioned on the bottom of the keeper body machined from one piece ofsoft magnetic material. Therefore the process of welding a root to akeeper body can be omitted. As a result of this, elevated strength andthe lower manufacturing cost are realized.

The root comprises the smaller diameter part and the larger diameterpart, and there is inevitably a step part between them. Furthermore onthe outer side of the larger diameter part there are the multiplecircumferential grooves. So, in this keeper, dental resin used to beembedded between the keeper and tooth root gets strongly meshed togetherwith the step part and the circumferential grooves. Therefore thiskeeper can be anchored more strongly thus elevating the prevention ofcoming off.

Accordingly the present invention provides a keeper of dental magneticattachment that is low in manufacturing cost, high in prevention ofcoming off, and high in strength.

BRIEF DESCRIPTIOPN OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will become readily apparent with reference to thefollowing detailed description, particularly when considered inconjunction with the companying drawings, in which:

FIG. 1 is a perspective view of a keeper of the first embodiment;

FIG. 2 is an illustration of an installation of the keeper of the firstembodiment;

FIG. 3 is an illustration of the structure of the dental magneticattachment of a prior art; and

FIG. 4 is a perspective view of a keeper of a prior art.

DESCRIPTION OF THE PREFERD EMBODIMENTS

In this invention, as mentioned above, the root consists of a smallerdiameter part and a larger diameter part. Controlling proper strength ofthe smaller diameter part enables the smaller diameter to be bent. Inthis case, it is easy to change the angle between a root and a keeperbody to a desired angle. For example, in the case that a tooth root istilted and its canal is also tilted, the root can be adjusted to theangle of the canal by bending the smaller diameter part of the root.Therefore the present keeper can be adaptable to any shape of a toothroot.

It is preferable that the circumferential grooves made on the largerdiameter part of the root take the form of a screw thread that windsspirally. That is to say, it is preferred to make the larger diameterpart itself male screw like. In this case, more circumferential groovescan be made enabling improvement of anchoring. Additionally, in the casethat it is necessary to take the keeper off the tooth root, it can betaken out little by little by rotating the whole keeper along the screwthread. Therefore in case it is necessary to take a keeper out of theoral cavity, it is possible to take out the whole keeper easily.

It is preferable that a body groove is made circumferentially on theouter side of the keeper body.

In this case, dental resin that is embedded between the keeper body andthe tooth root meshes together with the body groove and yields anchoringeffect, thus elevating the prevention of coming off of the keeper.

Also, it is preferred that the outer side of the keeper body have atleast two places that are flat and that are parallel to the axialdirection so as to be able to be grasped by a tool. In this case, byfitting a tool to the places, rotating or other action can be doneaccurately.

It is preferred that the axial length of the smaller diameter part islonger than twice the external diameter of the smaller diameter part.This makes it easy to get a smooth bent condition when the smallerdiameter is bent. On the other hand, in the case that the axial lengthof the smaller diameter part is less than twice its external diameter,stress is concentrated to both ends of the smaller diameter part and itmakes it difficult to get smooth bent condition. As a result, there isthe danger of insufficient strength. Therefore the axial length of thesmaller diameter part is preferred to be at least 2.5 times greater thanthe external diameter of the smaller diameter part. It is best that thelength be at least 3 times the diameter. The limit of the length of thesmaller diameter part is naturally decided by the proper length of theroot.

The external diameter of the smaller diameter part is preferred to be0.6-1.2 mm. In the case that the external diameter of the smallerdiameter part is shorter than 0.6 mm, the strength is too weak anddurability of the keeper may be reduced. On the other hand, in the casethat the external diameter of the smaller diameter part is above 1.2 mm,it is difficult to bend the smaller diameter part.

The external diameter of the larger diameter part is preferred to belarger than the external diameter of the smaller diameter part by 0.2 mmor more. In the case that the external diameter difference between thesmaller diameter part and the larger diameter part is less than 0.2 mm,the anchoring effect by the step part between them is insufficient. Theexternal diameter of the larger diameter part is limited by the size ofthe canal made in the tooth root, and is usually 2 mm or less.

Also, the larger diameter part can have a taper part that gets smallertowards the tip. In this case, the root is more smoothly inserted intothe canal in the tooth root.

Preferred Embodiments

First Embodiment

The embodiments of the keeper for the dental magnetic attachmentaccording to the present invention will be described with reference toFIG. 1 and FIG. 2

The keeper 1, as shown in FIG. 3, is the keeper for the dental magneticattachment that is attracted by the magnetic assembly 91 embedded indenture 81.

The keeper 1 of this example comprises the keeper body 10 that is shapedlike a plate and the root 2 positioned on the bottom of the keeper body10. The keeper body 10 and the root 2 are machined from the same pieceof soft magnetic material.

In the root 2, a smaller diameter part 21 is linked with the largerdiameter part 22 whose external diameter is larger than an externaldiameter of the smaller diameter part 21, and the smaller diameter part21 is also linked to the bottom of the keeper body 10. The outer side ofthe larger diameter part 22 has multiple circumferential grooves 225.

Thereinafter the details will be described.

The keeper 1 is machined from a single piece of soft magnetic material,Fe-19Cr-2Mo-0.2Ti soft magnetic stainless steel. By this machiningprocess, as shown in FIG. 1, disc-like keeper body 10 and root 2, whichhas a smaller diameter part 21 and a larger diameter part 22, are formedas one body by machining.

In this example, as shown in the same figure, circumferential grooves225 take the form of a screw thread wound spirally on the largerdiameter part 22 of the root 2.

Furthermore, the outer side of the keeper body 10 has a body groove 15made by circumferential machining.

As for specific dimensions, an external diameter D1 of the keeper body10 is φ4.0 mm and a thickness T1 is 0.8 mm. A width W1 of the bodygroove 15 is 0.4 mm, and a depth B1 is 0.2 mm. A length L1 of thesmaller diameter part 21 is 2.0 mm and an external diameter D2 is φ0.75mm. A length L2 of the larger diameter part 22 is 5.0 mm and an externaldiameter D3 is φ1.4 mm.

Next, the embodiment of the installation structure of the present keeper1 will be described with reference to FIG. 2.

The structure shown in FIG. 2 is an example wherein the tooth root 83 isalmost vertical and the keeper 1 is embedded in the vertical canal 820.In this case as shown in FIG. 2, the keeper is used in a condition thatthe keeper body 10 is kept vertical to the root 2 without bending. Theroot 2 is inserted into the root canal 820 of the tooth root 83, and thekeeper 1 is firmly embedded in the tooth root 83 with the dental resin 3around the root 2 and the keeper body 10. In the case that tooth root 83is at an incline and root canal 820 is made at an incline, root 2 istilted with respect to the keeper body 10 by bending the smallerdiameter part 21 of root 2 according to the incline of root canal 820(not shown in the figure). Therefore, even if tooth root 83 is at anincline, the keeper body 10 is easily embedded in the horizontalcondition.

In the following the effects of present invention are described.

The keeper 1 for the dental magnetic attachment has a keeper body 10 androot 2 that are both made of a single soft magnetic material bymachining in one piece. Therefore the cost of the manufacturing process,in comparison with the prior process of welding a root on a keeper body,is reduced.

The present root 2 has a bendable smaller diameter part 21. Thereforethe angle of the root 2 to the keeper body 10 can be easily changed to adesirable condition. So such has an excellent adaptability to a variousshapes of a tooth root.

The root 2 has a step part 215 between the smaller diameter part 21 andthe larger diameter part 22. Furthermore the outer side of the largerdiameter part 22 has multiple circumferential grooves 25, which take theform of a spiral screw thread.

Also the outer side of the keeper body has, as mentioned above, the bodygroove 15.

Therefore when the step part 215, multiple circumferential grooves 25and groove 15 are firmly embedded in tooth root 83 with dental resinbetween the tooth root 83 and the keeper 1, the keeper 1 is extremelystrongly anchored.

As mentioned above, circumferential grooves 25 of the larger diameterpart 22 take the form of a spirally wound screw thread. If it isnecessary to remove the keeper 1 from the tooth root 83, the keeper 1can be removed from the tooth root by rotating keeper 1 about the axisof root 2, like loosening a screw. This enables the keeper 1 to beremoved relatively easily.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedhere.

1. A keeper for a dental magnetic attachment to be attracted by amagnetic assembly embedded in a denture base, the keeper comprising: akeeper body which is shaped like a plate, and a root that is positionedon the bottom of the keeper body, wherein the keeper body and the rootare made of a same soft magnetic material and are machined from a singlepiece of the soft magnetic material in one piece, wherein the root has asmaller diameter part that is linked to a larger diameter part whoseexternal diameter is larger than an external diameter of the smallerdiameter part, wherein the smaller diameter part is linked to the bottomof the keeper body, wherein the outer side of the larger diameter parthas multiple circumferential grooves that are made circumferentially,wherein the circumferential grooves that are made on the larger diameterpart of the root take the form of a screw thread, and wherein the outerside of the keeper body has a body groove that is madecircumferentially.
 2. A keeper for a dental magnetic attachmentaccording to claim 1, wherein an axial length of the smaller diameterpart is longer than twice an external diameter of the smaller diameterpart.
 3. A keeper for a dental magnetic attachment according to claim 1,wherein an external diameter of the smaller diameter part is from 0.6 mmto 1.2 mm.
 4. A keeper for a dental magnetic attachment according toclaim 1, wherein an external diameter of the larger diameter part islarger than an external diameter of the smaller diameter part by 0.2 mmor more.